Methods of cleaning surfaces of copper-containing materials, and methods of forming openings to copper-containing substrates

ABSTRACT

The invention encompasses a semiconductor processing method of cleaning a surface of a copper-containing material by exposing the surface to an acidic mixture comprising Cl − , NO 3   −  and F − . The invention also includes a semiconductor processing method of forming an opening to a copper-containing substrate. Initially, a mass is formed over the copper-containing substrate. The mass comprises at least one of a silicon nitride and a silicon oxide. An opening is etched through the mass and to the copper-containing substrate. A surface of the copper-containing substrate defines a base of the opening, and is referred to as a base surface. The base surface of the copper-containing substrate is at least partially covered by at least one of a copper oxide, a silicon oxide or a copper fluoride. The base surface is cleaned with a cleaning solution comprising hydrochloric acid, nitric acid and hydrofluoric acid to remove at least some of the at least one of a copper oxide, a silicon oxide or a copper fluoride from over the base surface.

TECHNICAL FIELD

[0001] The invention pertains to methods of cleaning surfaces ofcopper-containing materials. In particular embodiments, the inventionpertains to semiconductor processing methods of forming openings tocopper-containing substrates.

BACKGROUND OF THE INVENTION

[0002] Copper has a relatively high conductance compared to many otherelements, and accordingly can be desired for utilization as a wiringlayer in various circuitry applications. For instance, in semiconductorprocessing applications, it can be desired to provide copper wiringlayers as electrical paths to various integrated circuit components.

[0003] A difficulty in utilizing copper in semiconductor processingapplications is that it can be difficult to clean. For instance,copper-containing materials will frequently have a surface to whichelectrical connection with other conductive components is ultimately tooccur. Formation of such electrical connection will frequently involveproviding a conductive material over the surface of thecopper-containing material. The conductive material is intended tophysically contact the surface of the copper-containing material to forman electrical connection with the copper-containing material. However,if the surface of the copper-containing material is partially orentirely covered with debris, the physical connection of the conductivematerial and copper surface can be impaired. Such impairment can lead toattenuation of electrical current passing between the copper-containinglayer and the conductive material formed thereover.

[0004] It would be desirable to develop improved methods of cleaningcopper-containing surfaces to remove debris from over the surfaces priorto forming conductive materials thereon.

SUMMARY OF THE INVENTION

[0005] In one aspect, the invention encompasses a semiconductorprocessing method of cleaning a surface of a copper-containing materialby exposing the surface to an acidic mixture comprising Cl⁻, NO₃ ⁻andF⁻.

[0006] In another aspect, the invention includes a semiconductorprocessing method of forming an opening to a copper-containingsubstrate. Initially, a mass is formed over the copper-containingsubstrate. The mass comprises at least one of a silicon nitride and asilicon oxide. An opening is etched through the mass and to thecopper-containing substrate. A surface of the copper-containingsubstrate defines a base of the opening, and is referred to as a basesurface. The base surface of the copper-containing substrate is at leastpartially covered by at least one of a copper oxide, a silicon oxide ora copper fluoride. The base surface is cleaned with a cleaning solutioncomprising hydrochloric acid, nitric acid and hydrofluoric acid toremove at least some of the at least one of a copper oxide, a siliconoxide or a copper fluoride from over the base surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0008]FIG. 1 is a diagrammatic, fragmentary, cross-sectional side viewof a semiconductor wafer fragment at a preliminary step of a processingmethod of the present invention.

[0009]FIG. 2 is a view of the FIG. 1 wafer fragment shown at aprocessing step subsequent to that of FIG. 1.

[0010]FIG. 3 is a view of the FIG. 1 wafer fragment shown at aprocessing step subsequent to that of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful arts” (Article 1, Section 8).

[0012] The invention encompasses utilization of a mixture comprisingCl⁻, NO₃ ⁻ and F⁻ for cleaning surfaces of copper-containing materials.Such mixture can be formed by, for example, combining an HCl solution(which can be obtained as, for example, a 36% (by weight) solution ofHCl in water), an HF solution (which can be obtained as, for example, a49% (by weight) solution of HF in water), an HNO₃ solution (which can beobtained as, for example, a 70% (by weight) solution of HNO₃ in water)and H₂O. The acidic mixture can thus be a cleaning solution comprisinghydrochloric acid, nitric acid and hydrofluoric acid.

[0013] If the cleaning solution is made by mixing water with theabove-described 36% hydrochloric acid solution, 49% hydrofluoric acidsolution, and 70% nitric acid solution, the relative amounts of thecombined water and solutions can be, for example, as follows. Thehydrochloric acid solution can be provided to a concentration so thatthere are from about 2½ parts of water added per 1 part HCl solution toabout 10 parts of water added per 1 part of HCl solution. The nitricacid solution can be provided so that there are from about 75 parts ofwater added per 1 part nitric acid solution to about 300 parts of wateradded per 1 part nitric acid solution. The hydrofluoric acid solutioncan be provided so that there are from about 150 parts of water addedper 1 part hydrofluoric acid solution to about 600 parts of water addedper 1 part of hydrofluoric acid solution. A preferred composition willcomprise about 300 parts of water combined with about 60 parts of HClsolution, about 2 parts of nitric acid solution, and about 1 part ofhydrofluoric acid solution.

[0014] The mixtures formed by the above-described combinations willpreferably consist essentially of Cl⁻, NO₃ ⁻, and F⁻, together withequilibrium components of H₃O⁺ and H₂O. The equilibrium components ofH₃O⁺ and H₂O will be understood by persons of ordinary skill in the artto comprise chemicals in equilibrium with H₃O⁺ and H₂O, such as, forexample, OH— (i.e., the hydroxide anion). As is known to persons ofordinary skill in the art, there is some concentration of hydroxideanion present in aqueous solutions, even at acidic pHs. Another way ofdescribing a mixture of the present invention is as an aqueous mixturecomprising non-aqueous components consisting essentially of Cl⁻, NO₃ ⁻and F⁻, or, in particular embodiments, comprising non-aqueous componentsconsisting of Cl⁻, NO₃ ⁻ and F⁻. Such description considers theequilibrium components of H₃O⁺ and H₂O to be aqueous components of themixture. Yet another way of describing a mixture of the presentinvention is that such mixture is a solution in which the onlynon-hydroxide anions consist essentially of Cl⁻, NO₃ ⁻ and F⁻, or inparticular embodiments, consist of Cl⁻, NO₃ ⁻ and F⁻.

[0015] An advantage of using an acidic solution comprising Cl⁻, NO₃ ⁻and F⁻ for cleaning copper in semiconductor fabrication processes isthat such solution can remove a variety of common contaminants in asingle processing step. For instance, hydrochloric acid can removecopper oxides (such as, for example, Cu₂ 0 and CuO), hydrofluoric acidcan remove silicon oxides (for example, SiO₂), as well as copper oxides;and nitric acid can remove elemental copper. The acidic solution of thepresent invention can also remove copper fluorides (CuF and CuF₂).

[0016] A semiconductor processing method incorporating a copper cleaningprocedure encompassed by the present invention is described withreference to FIGS. 1-3.

[0017] Referring first to FIG. 1, a semiconductive material waferfragment 10 is illustrated at a preliminary processing step. Waferfragment 10 comprises a semiconductive material substrate 12 having acopper-containing material 14 formed thereover. Substrate 12 cancomprise, for example, a monocrystalline silicon wafer having variouslevels of circuitry formed thereover. To aid in interpretation of theclaims that follow, the terms “semiconductive substrate” and“semiconductor substrate” are defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove.

[0018] Copper-containing material 14 can comprise, for example, a copperalloy, a copper compound, or elemental copper, and can be formed by, forexample, sputter deposition. In particular embodiments,copper-containing material 14 will consist essentially of elementalcopper (or consist of elemental copper) and defines a wiring layer forconnecting various circuitry components (not shown) associated withfragment 10.

[0019] A mass 16 is formed over copper-containing material 14. Mass 16can comprise, for example, one or more insulative materials. Inparticular embodiments, mass 16 comprises at least one of a siliconnitride (for example, Si₃N₄) and a silicon oxide (for example, SiO₂ or adoped oxide, such as, for example, borophosphosilicate glass). The shownmass 16 comprises two layers 18 and 20 which are formed one atop theother. One of layers 18 and 20 can comprise a silicon oxide, and theother of the layers can comprise a silicon nitride. For instance, layer18 could consist essentially of Si₃N₄ (or in particular embodimentsconsist of Si₃N₄) and layer 20 could consist essentially of SiO₂ (or inparticular embodiments consist of SiO₂). Such layers 18 and 20 can beformed by, for example, chemical vapor deposition.

[0020] Referring to FIG. 2, an opening 22 is etched through mass 16, andspecifically is etched through both of layers 18 and 20. Opening 22 canbe formed by, for example, photolithographic processing wherein aphotoresist masking layer (not shown) is formed over mass 16 andpatterned to protect some of mass 16 while leaving a portion of mass 16exposed to etching conditions which ultimately form opening 22.

[0021] Opening 22 extends to an upper surface 15 of copper-containingmaterial 14. Surface 15 defines a base of opening 22, and the portion ofsurface 15 within opening 22 can be referred to as a base surface.

[0022] Base surface 15 is partially covered by contaminating particles24. Such contaminating particles can comprise, for example, one or moreof a copper oxide, a silicon oxide, or a copper fluoride. Additionally,particles 24 can comprise elemental copper leftover from a sputterdeposition of copper-containing material 14. The copper oxide, siliconoxide or copper fluoride particles can be formed, for example, duringthe etch through layers 18 and 20. For instance, the silicon oxide canbe formed by either oxidation of a silicon nitride component of mass 16,or by debris occurring during the etch of a silicon oxide component ofmass 16. As another example, copper oxide can be formed from portions ofcopper-containing material 14 exposed to etching conditions, if suchconditions comprise oxidative components. As yet another example, copperfluoride can be formed from portions of copper-containing material 14exposed to etching conditions if such conditions comprise afluorine-containing etchant such as, for example, CF₄.

[0023] Although base surface 15 is shown to be only partially covered bycontaminating particles 24, it is to be understood that such particlescan entirely cover base surface 15. The particles 24 can also bedeposited on the sidewalls of opening 22 and on the surface of 20.

[0024] Although the contaminating particles 24 are described as beingformed during formation of opening 22, it is to be understood thatparticles 24 could be formed during other processing steps, such as, forexample, as residuals from a chemical-mechanical polishing processingstep.

[0025] Referring to FIG. 3, contaminating particles 24 (FIG. 2) areremoved from base surface 15 by cleaning such surface with an acidicmixture comprising Cl⁻, NO₃ ⁻ and F⁻. More specifically, base surface 15is cleaned by exposing the surface to the mixture of the presentinvention which is described above for removing copper oxide, siliconoxide, copper fluoride, and elemental copper from over base surface 15in one cleaning step. Such cleaning solution preferably is an aqueousmixture comprising non-aqueous components, with the non-aqueouscomponents consisting essentially of Cl⁻, NO₃ ⁻ and F⁻. The cleaningmixture can have such preferred composition at least until base surface15 is exposed to the mixture. Once base surface 15 is exposed to themixture, a composition of the mixture can change to include componentsreleased from particles 24 (FIG. 2) during the removal of particles 24from over base surface 15 with the mixture. The exposure of base surface15 to an acidic mixture comprising Cl⁻, NO₃ ⁻ and F⁻ can occur for atime of from about 30 seconds to about one hour at a temperature of fromabout 10° C. to about 40° C., and at atmospheric pressure. Thetemperature can comprise, for example, room temperature (typically from20° C. to 26° C.). Relative amounts of F⁻, Cl⁻ and NO₃ ⁻ within anacidic cleaning mixture of the present invention can be varied dependingupon particular cleaning conditions. For instance, if a large amount ofsilicon oxide contamination is expected to be present, the concentrationof F⁻ can be increased relative to the concentrations of Cl⁻ and NO₃ ⁻.On the other hand, if elemental copper is particularly problematic, theconcentration of NO₃ ⁻ can be increased relative to the concentrationsof Cl⁻ and F⁻. Further, if copper oxides are particularly problematic,the concentration of Cl⁻ can be increased relative to the concentrationsof NO₃ ⁻ and F⁻. Also, it can be desirable to increase the totalconcentrations of Cl⁻, NO₃ ⁻ and F⁻ to accomplish faster cleaning of acopper-containing substrate. Faster cleaning can also be accomplished byincreasing a temperature of the cleaning solution and/or a temperatureof the copper-containing material during a cleaning process.

[0026] Relative concentrations of Cl⁻, NO₃ ⁻ 0 and F⁻ can also be variedto avoid having one or more of the various anions etchingnon-contaminating portions of wafer fragment 10. For instance, a methodof exposing base surface 15 to a cleaning solution of the presentinvention is to dip a wafer comprising fragment 10 into a cleaningsolution of the present invention for a time of about 5 minutes. Suchdip would expose layers 18 and 20 to the cleaning solution, as well asexposing base surface 15 to the cleaning solution. If one or both oflayers 18 and 20 comprise silicon dioxide, the silicon dioxide would beexpected to be etched by F⁻ 0 present in the cleaning solution. Suchetching could alter a configuration of layers 18 and 20 if theconcentration of F⁻ were sufficiently high, or if the time of exposurewere sufficiently long. For instance, if an interface 19 is defined at alocation where layers 18 and 20 join, and if it is considered that oneof layers 18 and 20 is silicon nitride and the other is silicon dioxide,then the exposure to F⁻ in the cleaning solution may form divots atlocations 21 where interface 19 is exposed along sidewalls of opening22. A method of avoiding such divot formation is to adjust aconcentration of F⁻ within the cleaning solution so that the F⁻concentration is only enough to remove contaminating particles 24 frombase surface 15. In other words, to adjust the concentration of F⁻within the cleaning solution so that there is enough F⁻ to removeparticles 24, but not enough to detrimentally affect exposed siliconoxide surfaces of mass 16 during the time of an etch.

[0027] Preferably, if a silicon oxide containing surface of mass 16 isexposed to an acidic cleaning solution of the present invention during acleaning of base surface 15, the concentration of F⁻ within the acidicmixture will be such that less than 5 Angstroms of silicon oxide isremoved from the exposed surface of mass 16 during the cleaning of thebase surface.

[0028] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A semiconductor processing method of cleaning a surface of acopper-containing material, comprising: forming the copper-containingmaterial over a semiconductor substrate; and exposing the surface of thecopper-containing material to an acidic mixture comprising Cl⁻, NO₃ ⁻and F⁻.
 2. The method of claim 1 wherein the copper-containing materialconsists essentially of copper.
 3. The method of claim 1 wherein themixture is an aqueous mixture comprising non-aqueous components, andwherein the non-aqueous components consist essentially of Cl⁻, NO₃ ⁻,F⁻, at least until the exposing.
 4. The method of claim 1 wherein themixture is an aqueous mixture and wherein the only non-hydroxide anionsin the mixture consist essentially of Cl⁻, NO₃ ⁻ and F⁻, at least untilthe exposing.
 5. The method of claim 1 wherein the exposing occurs for atime of from about 30 seconds to about 1 hour.
 6. The method of claim 1wherein the exposing removes one or more of a copper oxide, a siliconoxide and a copper fluoride from on the surface.
 7. The method of claim1 wherein the exposing occurs at a temperature of from about 10° C. toabout 40° C.
 8. A method of cleaning a surface of a copper-containingmaterial, comprising: forming the copper-containing material over asemiconductor substrate; and exposing the surface of thecopper-containing material to a cleaning solution formed fromhydrochloric acid, nitric acid and hydrofluoric acid.
 9. The method ofclaim 8 wherein the cleaning solution consists essentially of Cl⁻, NO₃⁻, F⁻ and equilibrium components of H₃ ⁺ and H₂O, at least until theexposing.
 10. The method of claim 8 wherein the mixture is an aqueousmixture and wherein the only non-hydroxide anions in the cleaningsolution consist essentially of Cl⁻, NO₃ ⁻ and F⁻, at least until theexposing.
 11. The method of claim 8 further comprising, before theexposing, forming the cleaning solution by combining an HCl solution(36%, by weight in water), an HF solution (49%, by weight in water), anHNO₃ solution (70%, by weight in water) and H₂O; the relative amounts ofthe combined H₂O and solutions being: from about 2.5 parts H₂O per 1part HCl solution to about 10 parts H₂O per 1 part HCl solution; fromabout 75 parts H₂O per 1 part HNO₃ solution to about 300 parts H₂O per 1part HNO₃ solution; and from about 150 parts H₂O per 1 part HF solutionto about 600 parts H₂O per 1 part HF solution.
 12. The method of claim 8further comprising, before the exposing, forming the cleaning solutionby combining H₂O with solutions of HCl (36%, by weight in water), HF(49%, by weight in water) and HNO₃ (70%, by weight in water); therelative amounts of the combined H₂O and solutions being about 300 partsH₂O; about 60 parts of the HCl solution; about 2 parts of the HNO₃solution; and about 1 part of the HF solution.
 13. The method of claim 8wherein the exposing removes one or more of a copper oxide and a copperfluoride from on the surface.
 14. A semiconductor processing method offorming an opening to a copper-containing substrate, comprising:providing a copper-containing substrate having a mass thereover, themass comprising at least one of a silicon nitride and a silicon oxide,the copper-containing substrate being supported by a semiconductormaterial; etching an opening through the mass and to thecopper-containing substrate, a surface of the copper-containingsubstrate forming a base of the opening and thus defining a base surfaceof the opening, said base surface being at least partially covered by atleast one of a copper oxide, a silicon oxide or a copper fluoride; andcleaning said base surface with an acidic mixture comprising Cl⁻, NO₃ ⁻and F⁻ to remove at least some of the at least one of a copper oxide, asilicon oxide or a copper fluoride from the base surface.
 15. The methodof claim 14 wherein the mass comprises at least two layers stacked atopone another, one of the at least two layers comprising the silicon oxideand the other of the at least two layers comprising the silicon nitride;and wherein the opening is etched through both of the at least twolayers.
 16. The method of claim 14 wherein the base surface is at leastpartially covered by copper oxide, silicon oxide and copper fluoride;and wherein the cleaning removes substantially all of the copper oxide,silicon oxide and copper fluoride from the base surface of thecopper-containing substrate.
 17. The method of claim 14 wherein thecopper-containing substrate consists essentially of elemental copper.18. The method of claim 14 wherein the mixture is an aqueous mixturecomprising non-aqueous components, and wherein the non-aqueouscomponents consist essentially of Cl⁻, NO₃ ⁻, F⁻, at least until theexposing.
 19. The method of claim 14 wherein the mixture is an aqueousmixture and wherein the only non-hydroxide anions in the mixture consistessentially of Cl⁻, NO₃ ⁻ and F⁻, at least until the exposing.
 20. Asemiconductor processing method of forming an opening to acopper-containing substrate, comprising: providing a copper-containingsubstrate having a mass thereover, the mass comprising at least one of asilicon nitride and a silicon oxide, the copper-containing substratebeing supported by a semiconductor material; etching an opening throughthe mass and to the copper-containing substrate, a surface of thecopper-containing substrate forming a base of the opening and thusdefining a base surface of the opening, said base surface being at leastpartially covered by at least one of a copper oxide, a silicon oxide ora copper fluoride; and cleaning said base surface with a cleaningsolution formed from hydrochloric acid, nitric acid and hydrofluoricacid to remove at least some of the at least one of a copper oxide, asilicon oxide or a copper fluoride from the base surface.
 21. The methodof claim 20 wherein the mass comprises at least two layers stacked atopone another, one of the at least two layers comprising the silicon oxideand the other of the at least two layers comprising the silicon nitride;and wherein the opening is etched through both of the at least twolayers.
 22. The method of claim 20 wherein the base surface is at leastpartially covered by copper oxide, silicon oxide and copper fluoride;and wherein the cleaning removes substantially all of the copper oxide,silicon oxide and copper fluoride from the base surface of thecopper-containing substrate.
 23. The method of claim 20 wherein thecopper-containing substrate consists essentially of elemental copper.24. The method of claim 20 wherein the cleaning solution consistsessentially of Cl⁻, NO₃ ⁻, F⁻ and equilibrium forms of H₃ ⁺ and H₂O, atleast until the exposing.
 25. The method of claim 20 wherein the mixtureis an aqueous mixture an d wherein the only non-hydroxide anions in thecleaning solution consist essentially of Cl⁻, NO₃ ⁻ and F⁻, at leastuntil the exposing.
 26. The method of claim 20 further comprising,before the exposing, forming the cleaning solution by combining an HClsolution (36%, by weight in water), an HF solution (49%, by weight inwater), an HNO₃ solution (70%, by weight in water) and H₂O; the relativeamounts of the combined solutions and H₂O being: from about 2.5 partsH₂O per 1 part HCl solution to about 10 parts H₂O per 1 part HClsolution; from about 75 parts H₂O per 1 part HNO₃ solution to about 300parts H₂O per 1 part HNO₃ solution; and from about 150 parts H₂O per 1part HF solution to about 600 parts H₂O per 1 part HF solution.